Commercial aircraft typically include a satellite antenna for establishing a communication link with one or more geosynchronous satellites. The satellites may be a direct broadcast satellite (DBS) for providing television programming or a fixed satellite service (FSS) providing Internet access, for example. A DBS satellite operates within 12.2-12.7 GHz, and a FSS satellite operates within 11.7-12.2 GHz. These frequencies are within the Ku-band.
An antenna assembly carried by the aircraft includes a radome to protect the satellite antenna and associated equipment from environmental exposure. The radome needs to be strong to withstand the aerodynamic loads of the aircraft while meeting desired electrical performance characteristics. A bandwidth of a Ku-band satellite antenna compatible with DBS or FSS satellites is about 0.5 GHz. A radome compatible with the Ku-band typically includes a thin laminate skin, low density core, sandwich design. Since the bandwidth is relatively narrow, this type of radome is relatively straightforward to design to meet desired structural and electrical performance characteristics.
Airborne satellite communication links are currently being developed for K-band frequencies and Ka-band frequencies to achieve broad bandwidths for high data rates. The K-band covers 18-27 GHz and the Ka-band covers 27-40 GHz. A bandwidth of a K-band/Ku-band satellite antenna is about 22 GHz. As a result of such a wide bandwidth, it becomes more difficult to design a K-band/Ku-band radome to meet desired structural and electrical performance characteristics.
One approach for a K-band/Ku-band radome is disclosed in U.S. published patent application no. 2013/0321236. A sandwich radome structure includes a central core layer, a reinforced laminate skin adjacent each side of the central core, and outer matching layers on each of the reinforced laminates. The central core layer may include a syntactic film material with a density of 32 to 42 PCF and a relative dielectric constant range of 1.6 to 2.3. The laminate skins may include a quartz woven fabric reinforcement and a thermo-set resin. The outer matching layers may include thermo-set resin and glass bubbles with a relative dielectric constant in the range of 1.6 to 2.3. A thickness of each layer may be a multiple of a quarter wavelength at approximately the center frequency over the incidence angle range of the radome frequency range. This design is also applicable to Ku-band/K-band/Ka-band radome designs.
Another radome design is disclosed in U.S. Pat. No. 7,420,523. The radome structure includes a structural layer including plies of fibers in a resin matrix, an inside matching layer adjacent to one side of the structural layer, and an outside matching layer adjacent to the opposite side of the structural layer. Both matching layers have a dielectric constant lower than a dielectric constant of the structural layer and are made of formable sheet material assembled with the structural layer during shaping of the radome and co-cured with the structural layer resulting in a rigid final form of the radome. The matching sheet layer material during assembly includes an uncured thermoset resin with a plurality of gas-filled microspheres therein to reduce the dielectric constant of the matching layers.
Even in view of the above radomes, there is still a need to provide alternative designs for a multi-band radome that operates over a wide bandwidth while meeting desired structural and electrical performance characteristics.
If the radome is to cover more than one satellite antenna, then weight becomes a concern since the size of the antenna assembly will increase accordingly. As an example, an existing antenna assembly for a single satellite antenna is based on a fixed attachment method that includes a large metal plate that is coupled to the fuselage of the aircraft. The metal plate includes a number of spaced apart fittings that are then coupled to the radome. The use of a metal plate is bulky and heavy. Although such a metal plate sized for a single satellite antenna may be acceptable, it becomes weight prohibitive when increased in size to cover more than one satellite antenna. Consequently, there is also a need to provide a light weight antenna assembly.